Chromatography is a separation technique used to separate compositions from each other based on the affinity of each compound, in a mixture of compounds held in a solution, for or to a media through which the composition is moving in relation to. The media is normally held stationary and is sometimes referred to as the stationary phase. The media is normally a bed of particles or beads or a porous monolith. The solution moving through the media is often referred to as the mobile phase. The mobile phase can be a gas or a liquid or a gas held at a critical pressure and temperature, or near critical or super critical pressures and temperatures. As used herein, the term “fluid” refers to all gases and liquids, and critical, near critical and supercritical fluids.
High performance liquid chromatography (HPLC) is performed in closed systems under pressure as is gas and critical, near critical and supercritical chromatographic techniques. These techniques have broad applications; for example, which certainly is not intended to be an exhaustive list, these techniques are used for drug discovery, chemical analysis, human and veterinary diagnostics, forensics, manufacturing, pharmaceutical processes, and quality control. The closed systems are comprised of pumps, valves, columns, tubing, detectors and the like.
The term “filtration” is used to refer to processes which separate materials on the basis of size rather than affinity.
The term “catalysis” is used to refer to processes in which one or more compounds form one or more reaction products in the presence of a further compound or material, the catalyst, which is not consumed in the process. An automotive catalytic converter is one example of a device in which one of more compounds form one or more reaction products in the presence of a catalyst immobilized on a solid support. A further example, without limitation, is an enzymatic reactor that catalyzes a reaction to form a reaction product. Enzymatic reactors are used in biochemical reactions, for example, to react proteins, polysaccharides, to amplify nucleic acids and the like.
Electrokinetic (EK) pumps are devices which use electro-osmosis to create fluid pressure and flow in conduits. EK pumps comprise a charged porous medium normally contained in a conduit. A voltage is applied across the porous media to induce electro-osmosis.
As used herein, the term “monolith” refers to a non-particulate block material. The block of material is a coalescence of polymeric compositions into a skeletal core and pores. Those skilled in the art characterize porous materials on the basis of the skeletal core, pores and/or interstitial volume. The skeletal core refers to the solid structural part of the material. The interstitial volume refers to the empty, non-solid, space, comprised of pores. In particulate beds, the term interstitial will include space between particles and pore volume. Monolith materials do not have space between particles because the materials are non-particulate. The term as applied to monolith materials, as used herein, refers to the pore volume.
Porous monolith materials tend to be fragile. Porous monolith materials tend to shrink upon polymerization. The monolith materials tend to separate from walls of housings to form channels along the exterior of the materials, and fracture to form internal channels. These channels are different in character from the pores through which fluid would otherwise flow. The pores are normally of a consistent size and have a random pattern. The channels are larger and have a non-random mechanical stress determined pattern. The channels influence the flow of fluids through the materials.
Fluids which are pumped into the porous monoliths will flow through the path of least resistance. If channels or cracks are present, the fluid will preferentially pass through the channels and bypass the porous material. In separation chemistry, filtration and catalysis such flows lead to unpredictable or incomplete separations, filtrations or catalysis.
With respect to EK pumps, channels in the medium can result in poor pump performance and failure.